1. Field of the Invention
The present invention relates to a modified electrode for anodic stripping analysis. Particularly, it is relates to a modified electrode which containing mercury oxide as built-in mercury precursor.
2. Discussion of Related Art
Anodic stripping analysis has been known as one of the most sensitive techniques and widely used for trace heavy metal analysis in various samples because of its capability of preconcentration of analytes on the surface of the electrode.
In general, mercury electrodes such as the hanging mercury drop electrode (HMDE) or thin-film mercury electrode (TFME) have been used for anodic stripping analysis because of their distinctive analytical characteristics. However, use of the hanging mercury drop electrode has been hesitated due to the difficulties in handling liquid mercury and disposing of used mercury. Hence, use of the thin-film mercury electrode is preferred because of its improved convenience and sensitivity. If the thin-film mercury electrode used along with fast scan stripping voltammetric techniques, cumbersome deoxygenation step can be skipped. Although the improved sensitivity and analytical convenience of the thin-film mercury electrode may still attract analysts to choose the stripping analysis technique for trace heavy metal analysis in laboratories or in the field, a film generation step either from a solution of Hg.sup.2+ or in situ by addition of Hg.sup.2+ to sample solutions should be always involved. A drawback of the thin-film mercury electrode is instability of mercury thin-film formed at the surface of glassy carbon electrodes, which affects the reproducibility of analysis. Although there have been extensive studies on the improvement of the stability of mercury film, it is not satisfactory yet.
General modified composite electrodes are disclosed in U.S. Pat. No. 4,957,593 and U.S. Pat. No. 5,002,651.
According to the U.S. Pat. No. 4,957,593, the modifiers of the disclosed modified composite electrodes may provide the characteristics of electroactivity, inclusion, adsorption or electrocatalysis to the surface of the electrode in a solution. Also, after use, the electrode surface may be renewed by removing the surface portion deactivated and thereby exposing a fresh portion of the uniform electrode matrix.
According to the U.S. Pat. No. 5,002,651, the renewable composite microelectrodes for electrochemical applications are formed by an initial coating on an elongated conductive substrate of less than 500 micrometers over at least a portion of its length with a modifier composition, and superposed coating of electronically resistive polymer. The microelectrode will normally be used with only the tip portion thereof immersed in the solution, and it may be renewed by removing the contaminated tip portion.